1. Field of the Invention
The present invention relates to a zoom lens system, an imaging device, and a camera. In particular, the present invention relates to: a zoom lens system which has, as well as a high performance, a small size and a small F-number at a wide-angle limit, and is satisfactorily adaptable for wide-angle image taking; an imaging device employing the zoom lens system; and a camera employing the imaging device.
2. Description of the Background Art
With recent progress in the development of solid-state image sensors such as CCD (Charge Coupled Device) and CMOS (Complementary Metal-Oxide Semiconductor) having high pixel density, digital still cameras and digital video cameras (simply referred to as “digital cameras”, hereinafter) are rapidly spreading, which employ an imaging device including an imaging optical system of high optical performance corresponding to the solid-state image sensors having high pixel density. Among the digital cameras having high optical performance, compact digital cameras are increasingly demanded.
For the purpose of easy transportation, further size reduction of the above-mentioned digital cameras is required. Various proposals have been made to realize such compact digital cameras.
For example, there has been proposed a zoom lens, in order from the object side to the image side, comprising a front unit having negative optical power as a whole, and a rear unit having positive optical power as a whole. In the zoom lens, in zooming from a wide-angle limit to a telephoto limit, a lens unit located closest to the object side moves. The zoom lens includes a lens unit having an aperture diaphragm arranged between lens elements, the air space between which is not varied during zooming. A part of lens units included in the rear unit is moved to compensate image blur.
Japanese Laid-Open Patent Publication No. 2006-133582 discloses a zoom lens, in order from the object side to the image side, comprising five lens units of positive, negative, positive, positive, and positive, which move in zooming. In the zoom lens, a diaphragm is arranged between lenses constituting the third lens unit. A part of the third lens unit moves in a direction perpendicular to the optical axis to compensate image blur.
Japanese Laid-Open Patent Publication No. 2009-162862 discloses a zoom lens, in order from the object side to the image side, comprising four lens units of positive, negative, positive, and positive, which move in zooming. In the zoom lens, a diaphragm is arranged between lenses constituting the third lens unit. A part of the third lens unit moves in a direction perpendicular to the optical axis to compensate image blur.
Japanese Laid-Open Patent Publication No. 2010-014844 discloses a zoom lens, in order from the object side to the image side, comprising four lens units of positive, negative, positive, and positive, which move in zooming. In the zoom lens, a diaphragm is arranged between lenses constituting the third lens unit. The entire third lens unit moves in a direction perpendicular to the optical axis to compensate image blur.
Japanese Laid-Open Patent Publication No. 2010-033087 discloses a zoom lens, in order from the object side to the image side, comprising four lens units of positive, negative, positive, and positive, which move in zooming. In the zoom lens, a diaphragm is arranged between lenses constituting the third lens unit. A part of the third lens unit moves in a direction perpendicular to the optical axis to compensate image blur.
Japanese Laid-Open Patent Publication No. 11-231220 discloses a zoom lens, in order from the object side to the image side, comprising four lens units of negative, positive, positive, and positive, which move in zooming. In the zoom lens, a diaphragm is arranged between lenses constituting the third lens unit. A part of the third lens unit moves in a direction perpendicular to the optical axis to compensate image blur.
However, in the zoom lens disclosed in Japanese Laid-Open Patent Publication No. 2006-133582, the maximum view angle at a wide-angle limit is only about 60°, which does not satisfy the requirements for compact digital cameras whose view angle at a wide-angle limit has been increased in recent years. Since the overall lens length is fixed, the front lens diameter is increased. Further, since the back focal length is long, the overall lens length is increased, resulting in insufficient size reduction.
In the zoom lens disclosed in Japanese Laid-Open Patent Publication No. 2009-162862, the maximum view angle at a wide-angle limit is 70°. However, the ratio of the overall lens length to the image height is as high as 20 or more, which results in insufficient size reduction.
In the zoom lens disclosed in Japanese Laid-Open Patent Publication No. 2010-014844, the maximum view angle at a wide-angle limit is 79°. However, since the entire third lens unit is moved in the direction perpendicular to the optical axis to compensate image blur, the size of the mechanism for this movement is increased. Further, the minimum F-number is 3.28, which does not satisfy the requirements for bright lenses.
In the zoom lens disclosed in Japanese Laid-Open Patent Publication No. 2010-033087, the ratio of the overall lens length to the image height is as high as 20 or more, which results in insufficient size reduction. Further, the maximum view angle at a wide-angle limit is only 60°, which does not satisfy the requirements for compact digital cameras whose view angle at a wide-angle limit has been increased in recent years.
In the zoom lens disclosed in Japanese Laid-Open Patent Publication No. 11-231220, the maximum view angle at a wide-angle limit is 73°. However, the maximum F-number is as large as 3.8, which does not satisfy the requirements for brighter lenses. Further, since the back focal length is long, sufficient size reduction cannot be achieved.